As an X-ray detection apparatus used in an X-ray computed tomography apparatus, a photon counting type X-ray detection apparatus for measuring the energy of X-rays is known. As a photon counting type X-ray detection apparatus, there is an SiPM (Silicon Photo-Multiplier). The SiPM includes a plurality of detector pixels. Each detector pixel includes a scintillator and a plurality of APD (Avalanche Photo-Diode) cells. The scintillator converts incident X-rays into a plurality of scintillation photons. The plurality of scintillation photons are received by the plurality of APD cells. In a Geiger mode, each APD cell causes an electron avalanche (ignites) in response to one or more scintillation photons to generate a current pulse of a predetermined pulse height or charge amount independent of the number of scintillation photons. The number of APD cells that ignite depends on the number of scintillation photons (that is, the energy of the incident X-rays). A plurality of current pulses from the plurality of APD cells are integrated into one current pulse (output pulse). When the pulse height or charge amount of the output pulse is measured, the energy of the incident X-rays can be measured.
When the APD cells ignite in response to the scintillation photons, they need to be charged to be ignitable again. If the dose of X-rays that enter the SiPM is excessive, charging of the APD cells delays. If the insufficiently charged APD cells ignite, the apparent pulse height of the output pulse lowers. If this phenomenon occurs, it is impossible to make discrimination between a pulse height caused by undercharging and a truly low pulse height. The pulse height of the output pulse is an important physical quantity that decides the energy of X-rays. For this reason, it can be said that an X-ray detection apparatus that can cause lowering of a pulse height due to undercharging is not very reliable in terms of the accuracy of energy resolution.